The present invention relates to a screen apparatus for refining a papermaking material, wherein clinging and crushing, i.e. pulverization, of foreign materials contained in the papermaking material can be prevented.
Heretofore, as an apparatus with a plurality of screens for separating and treating foreign materials contained in a papermaking material, i.e. old paper, for example, Japanese Patent Publication (KOKOKU) No. 59-32594 may be mentioned.
In a pressure type papermaking composite screen disclosed in the above Japanese Patent Publication, there is no problem when a papermaking material which has been pre-treated to remove certain large foreign materials, such as vinyl sheets and strings, is fed to the pressure type composite screen.
However, in case the papermaking material containing the certain large foreign materials, such as vinyl sheets and strings, without the pre-treatment is subjected to a treatment by the pressure type papermaking composite screen, the foreign materials contained in the papermaking material are clung to a rotating center portion of impellers, since the impellers are located in front of a screen through which the papermaking material passes first, and openings are provided across the screen except for a portion through which a main shaft for rotating the impellers is provided, so that the papermaking material flows toward the openings.
If the foreign materials cling to the center portion of the impellers, there is a problem such that the foreign materials are crushed or pulverized by the impellers, so that the crushed foreign materials are contained in good fibers in the papermaking material to thereby have to remove the crushed foreign materials in a later step.
In view of the above, the present invention has been made, and an object of the invention is to provide a screen apparatus, wherein clinging of foreign materials and crushing thereof can be suppressed or prevented to thereby refine a papermaking material.
Another object of the invention is to provide a screen apparatus as stated above, wherein refining effects can be increased.
Further objects and advantages of the invention will be apparent from the following description of the invention.